Germanium (Ge) is a semiconductor that has better electrical properties than silicon (Si). However, germanium oxide (for example, GeO2) is unstable. Therefore, the germanium oxide is rarely used for a semiconductor material forming a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
For example, non-patent documents 1 and 2 disclose that an aluminum nitride (AlN) film is used as a part of a gate insulating film. A dielectric constant of the aluminum nitride film is higher than that of silicon oxide (SiO2) film. It is therefore possible to reduce an EOT (Equivalent Oxide Thickness) of the aluminum nitride film. When a miniaturization of a gate length is performed, reduction of the EOT is important.